tmpnam
Defined in header
<stdio.h>
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char *tmpnam( char *filename );
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Creates an unique filename and stores it in character string pointed to by filename
. The function is capable of generating up to TMP_MAX of unique filenames, but some or all of them may be in use in the filesystem and thus not suitable return values.
tmpnam
is not reentrant and thus not thread-safe.
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[edit] Parameters
filename | - | pointer to the character string to be used as a result buffer. If NULL is passed, a pointer to an internal static buffer is returned.
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[edit] Return value
filename
if filename
was not NULL. Otherwise a pointer to an internal static buffer is returned. If no suitable filename can be generated, NULL is returned.
[edit] Notes
Although the names generated by tmpnam
are difficult to guess, it is possible that a file with that name is created by another process between the moment tmpnam
returns and the moment this program attempts to use the returned name to create a file. The standard function std::tmpfile and the POSIX function mkstemp do not have this problem.
POSIX systems additionally define the similarly named function tempnam()
, which offers the choice of a directory (which defaults to the optionally defined macro P_tmpdir)
[edit] Example
tmpnam with error checking. Code generates a unique filename.
#include <stdlib.h> #include <stdio.h> int main(void) { printf("TMP_MAX = %d\n", TMP_MAX); printf("L_tmpnam = %d\n", L_tmpnam); char buffer[L_tmpnam] = {'\0'}; char * fname = tmpnam(buffer); if (fname == NULL) { perror("tmpnam()"); fprintf(stderr,"tmpnam() failed in file %s at line # %d\n", __FILE__,__LINE__-4); exit(EXIT_FAILURE); } printf("%s\n", fname); printf("%s\n", buffer); printf("\n"); /* Argument is a null pointer. */ char * fn1 = tmpnam(NULL); printf("%s\n", fn1); printf("%p\n", fn1); /* Subsequent calls to tmpnam modify the same object. */ char * fn2 = tmpnam(NULL); printf("%s\n", fn2); printf("%p\n", fn2); exit(EXIT_SUCCESS); }
Output:
TMP_MAX = 238328 L_tmpnam = 20 /tmp/filer8fER3 /tmp/filer8fER3 /tmp/fileurN5sQ 0x7f0f05dc7a10 /tmp/file1Pux4C 0x7f0f05dc7a10
[edit] See also
returns a pointer to a temporary file (function) |
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C++ documentation for tmpnam
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